From: Rusty Russell <rusty@rustcorp.com.au>
To: Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>
Cc: Dmitry Antipov <dmitry.antipov@linaro.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
patches@linaro.org, linaro-dev@lists.linaro.org
Subject: Re: [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR
Date: Tue, 31 Jan 2012 15:18:54 +1030 [thread overview]
Message-ID: <87obtkjx3d.fsf@rustcorp.com.au> (raw)
In-Reply-To: <20120130181639.GJ3355@google.com>
On Mon, 30 Jan 2012 10:16:39 -0800, Tejun Heo <tj@kernel.org> wrote:
> On Mon, Jan 30, 2012 at 12:12:18PM -0600, Christoph Lameter wrote:
> > > I thought it didn't. I rememer thinking about this and determining
> > > that NULL can't be allocated for dynamic addresses. Maybe I'm
> > > imagining things. Anyways, if it can return NULL for valid
> > > allocation, it is a bug and should be fixed.
> >
> > I dont see anything that would hinder an arbitrary value to be returned.
> > NULL is also used for the failure case. Definitely a bug.
>
> Given the address translation we do and kernel image layout, I don't
> think this can happen on x86. It may theoretically possible on other
> archs tho. Anyways, yeah, this one needs improving.
I tried setting the lower bit on all percpu ptrs, but since non-dynamic
percpu vars could have odd alignments, that fails in general.
> > > We don't have returned addr >= PAGE_SIZE guarantee yet but I'm fairly
> > > sure that's the only acceptable direction if we want any improvement
> > > in this area.
> >
> > The ZERO_SIZE_PTR patch would not make the situation that much worse.
>
> I'm not objecting to marking zero-sized allocations per-se. I'm
> saying the patch is pointless at this point. It doesn't contribute
> anything while giving the illusion of better error checking than we
> actually do. Let's do it when it can actually work.
Disagree: This patch works. It allows zero-size per-cpu allocs, like
the other allocators. Nor does it fail in practice.
We should do better, but the perfect is the enemy of the good.
Cheers,
Rusty.
next prev parent reply other threads:[~2012-01-31 9:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 8:37 [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR Dmitry Antipov
2012-01-30 16:15 ` Christoph Lameter
2012-01-30 17:15 ` Tejun Heo
2012-01-30 17:19 ` Tejun Heo
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:33 ` Tejun Heo
2012-01-30 17:35 ` Christoph Lameter
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:42 ` Tejun Heo
2012-01-30 17:52 ` Christoph Lameter
2012-01-30 17:54 ` Tejun Heo
2012-01-30 17:58 ` Christoph Lameter
2012-01-30 18:02 ` Tejun Heo
2012-01-30 18:12 ` Christoph Lameter
2012-01-30 18:16 ` Tejun Heo
2012-01-31 4:48 ` Rusty Russell [this message]
2012-01-30 18:13 ` Tejun Heo
2012-01-30 18:15 ` Christoph Lameter
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